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<TITLE>80386 Programmer's Reference Manual -- Opcode BOUND</TITLE>
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<H1>BOUND -- Check Array Index Against Bounds</H1>

<PRE>
Opcode    Instruction          Clocks    Description

62 /r     BOUND r16,m16&16     10        Check if r16 is within bounds
                                         (passes test)
62 /r     BOUND r32,m32&32     10        Check if r32 is within bounds
                                         (passes test)
</PRE>

<H2>Operation</H2>

<PRE>
IF (LeftSRC < [RightSRC] OR LeftSRC > [RightSRC + OperandSize/8])
   (* Under lower bound or over upper bound *)
THEN Interrupt 5;
FI;
</PRE>

<H2>Description</H2>

BOUND ensures that a signed array index is within the limits specified by a
block of memory consisting of an upper and a lower bound. Each bound uses
one word for an operand-size attribute of 16 bits and a doubleword for an
operand-size attribute of 32 bits. The first operand (a register) must be
greater than or equal to the first bound in memory (lower bound), and less
than or equal to the second bound in memory (upper bound). If the register
is not within bounds, an Interrupt 5 occurs; the return EIP points to the
BOUND instruction.
<P>
The bounds limit data structure is usually placed just before the array
itself, making the limits addressable via a constant offset from the
beginning of the array.

<H2>Flags Affected</H2>

None

<H2>Protected Mode Exceptions</H2>

Interrupt 5 if the bounds test fails, as described above; #GP(0) for an
illegal memory operand effective address in the CS, DS, ES, FS, or GS
segments; #SS(0) for an illegal address in the SS segment; #PF(fault-code)
for a page fault
<P>
The second operand must be a memory operand, not a register. If BOUND is
executed with a ModRM byte representing a register as the second operand,
#UD occurs.

<H2>Real Address Mode Exceptions</H2>

Interrupt 5 if the bounds test fails; Interrupt 13 if any part of the
operand would lie outside of the effective address space from 0 to 0FFFFH;
Interrupt 6 if the second operand is a register

<H2>Virtual 8086 Mode Exceptions</H2>

Same exceptions as in Real Address Mode; #PF(fault-code) for a page fault


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Chapter 17 -- 80386 Instruction Set</A><BR>
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